(KRON) — The mother of the Oakland Zoo’s gray wolf pack was humanely euthanized Wednesday after a tumor was found in her abdomen, the zoo announced in a post on X, formerly Twitter. Zoo veterinarians discovered a large mass during a routine examination of the animal, which was named “Siskiyou.”

Following a CT scan, the zoo’s vet team determined that the tumor was untreatable. Because of the apparent pain and suffering the tumor was causing her, the zoo made the decision to euthanize her.

Following the euthanasia, the zoo’s Animal Care Team brought Siskiyou’s body back home “to give the pack time to understand her passing.”

Siskiyou came to Oakland Zoo in December 2017 from a conservation center in Montana, zoo officials said. At the Oakland Zoo California Trail, Siskiyou was introduced to a male gray wolf named Sequoia.

Photos: Oakland Zoo

She gave birth to four pups in 2019 and “the pack has enjoyed their sprawling habitat together for the past four and a half years,” the zoo said.

“Siskiyou has quite the life. From growing up in Montana, to raising 4 amazing offspring,” said one of the keepers who cared for the wolf. “In some sense, she came the farthest of all the wolves in the pack (both physically and psychologically). Her absence leaves a huge gap in our hearts and her family.”

Zoo officials say they will continue to monitor the rest of the gray wolf pack closely “as they absorb the loss of their matriarch.”

“Our hearts are with sweet Siskiyou, and the dedicated Animal Care team that cared for her with passion and love,” zoo officials said.